1. Field of Invention
The present invention relates to an electro-hydraulic valve train. More particularly, the present invention relates to an electro-hydraulic valve train that can change valve lift and valve opening/closing timing according to operation state of an engine.
2. Description of Related Art
An internal combustion engine generates power by burning fuel in a combustion chamber in air media drawn into the chamber. Intake valves are operated by a camshaft in order to intake the air, and the air is drawn into the combustion chamber while the intake valves are open. In addition, exhaust valves are operated by the camshaft, and a combustion gas is exhausted from the combustion chamber while the exhaust valves are open.
An optimal operation of the intake valves and the exhaust valves depends on a rotation speed of the engine. That is, an optimal lift or optimal opening/closing timing of the valves depends on the rotation speed of the engine. In order to achieve such an optimal valve operation depending on the rotation speed of the engine, various researches have been undertaken. For example, research has been undertaken for a variable valve lift (VVL) apparatus that enables different lifts depending on an engine speed, and for a variable valve timing (VVT) apparatus that opens/closes the valves with different timing depending on the engine speed.
Meanwhile, an electro hydraulic valve train (EHV) which controls close timing of a valve by using hydraulic pressure has been researched.
Such an EHV has advantages of controlling opening/closing timing of the valve by controlling release timing of the hydraulic pressure, but has drawbacks of requiring additional devices for controlling valve lift.
In addition, a hydraulic pump generates hydraulic pressure by operation of a camshaft, and the EHV, the hydraulic pump, and hydraulic pressure lines are provided above valves so as to supply the hydraulic pressure to the EHV. Therefore, an engine layout should be changed in order to apply a conventional EHV to the engine using a swing arm.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.